About Rationally Speaking

Rationally Speaking is a blog maintained by Prof. Massimo Pigliucci, a philosopher at the City University of New York. The blog reflects the Enlightenment figure Marquis de Condorcet's idea of what a public intellectual (yes, we know, that's such a bad word) ought to be: someone who devotes himself to "the tracking down of prejudices in the hiding places where priests, the schools, the government, and all long-established institutions had gathered and protected them." You're welcome. Please notice that the contents of this blog can be reprinted under the standard Creative Commons license.

Tuesday, February 18, 2014

The missing shade of blue

by Massimo Pigliucci

This semester I’m teaching a graduate level course on “Hume Then and Now,” which aims at exploring some of the original writings by David Hume, particularly the Enquiry Concerning Human Understanding, and contemporary philosophical treatments of Humean themes, such as induction, epistemic justification, and causality.

I want to talk here about a particular episode belonging to Section 2 of the Enquiry, where Hume introduces the famous problem of the missing shade of blue, which is still discussed today in philosophy of mind. I think reflection on the problem itself, as well as some attempts to reconcile what appears to be a glaring contradiction in Hume’s own treatment of it, tells us something interesting about how philosophy is done, and sometimes overdone.

To set the stage, let me tell you a bit about the broader Humean project first. Hume proposed nothing less than an overhaul of the way we do philosophy, largely in reaction to what he (correctly, in my mind) perceived as the useless and obscure musings of “the schoolmen” who preceded him and who were still influential at the onset of the 18th century.

A cardinal point of Hume’s novel approach to philosophy was going to be to conduct, as the title of the book clearly states, an inquiry into how human beings understand things, because only by appreciating human epistemic limits can we produce sound philosophical reasoning. (This approach still inspires plenty of philosophers today, and even a number of scientists, such as social psychologists Jonathan Haidt and Joshua Greene.)

Hume explicitly and very clearly sets out his program for his readers in Section 1 of the Enquiry, appropriately entitled “Of the different species of philosophy.” But it is Section 2, “Of the origin of ideas,” that concerns us here.

It begins with the introduction of Hume’s famous distinction between ideas and impressions. Ideas are thoughts, while impressions are sensations. The first are derived from memory and abstract thinking, the second from the senses. Ideas, Hume argues, are (weaker) “copies” of impressions, and impressions are obtained directly from experience.

For instance, we can feel love for someone (an impression) and we can think about the concept of love (an idea). Clearly, says Hume, the feeling is much stronger than the concept, as expected if it were derivative. Ultimately, according to Hume, all knowledge comes from experience, which is why he is classified among the British empiricists, like Locke (as opposed to the continental rationalists, like Spinoza and Leibniz) — even though Hume actually had a fairly low opinion of Locke, whom he saw as still confused by the influence of the schoolmen.

Hume acknowledges that it would seem that human imagination is boundless, as we can think about all sorts of things that don’t actually exist (and cannot therefore be experienced), such as unicorns and gods. But he then argues that no matter how apparently fanciful our imagination is, all our complex ideas are in fact combinations of simpler ones, and those in turn can be traced to our experience.

Take god, for instance: “The idea of God, as meaning an infinitely intelligent, wise, and good Being, arises from reflecting on the operations of our own mind, and augmenting, without limit, those qualities of goodness and wisdom.”

Hume gives two arguments in support of his thesis: first, whenever we analyze a complex idea — such as that of god — we find that it is, in fact, traceable to a combination of simpler ones, of which we ultimately have direct experience (we have all seen intelligent, wise, and good people). Second, we know that when people have a defect in their sensorial perception they are incapable of forming the corresponding ideas: a blind man has no concept of color, because he has never had an impression of what a color feels like through his senses.

And now we come to the problem caused by the missing shade (for those of you who are following the original text, this is #16 of Section 2 of the Enquiry). I’ll let Hume’s beautifully clear prose speak for itself here (the italics are mine, and they will come in handy during the discussion below):

“There is, however, one contradictory phenomenon, which may prove that it is not absolutely impossible for ideas to arise, independent of their correspondent impressions. ... Suppose, therefore, a person to have enjoyed his sight for thirty years, and to have become perfectly acquainted with colours of all kinds except one particular shade of blue, for instance, which it never has been his fortune to meet with. ... Now I ask, whether it be possible for him, from his own imagination, to supply this deficiency, and raise up to himself the idea of that particular shade, though it had never been conveyed to him by his senses? I believe there are few but will be of opinion that he can: and this may serve as a proof that the simple ideas are not always, in every instance, derived from the correspondent impression; though this instance is so singular, that it is scarcely worth our observing, and does not merit that for it alone we should alter our general maxim.”

Okay, so what’s the big deal, you say? Well, it doesn’t take a sophisticated Hume scholar to figure out that our hero here goes through the following strange sequence: 1. He comes up with what he says is a general principle concerning human understanding; 2. He finds an exception to that principle; 3. He the discards that apparently damning finding as not worthy of consideration. And this despite the fact that Hume had told his readers a bit earlier that the new philosophy he is proposing is subject to empirical disconfirmation, just like the natural philosophy (aka, science) by which it is inspired! What’s going on here? Plenty of commentators have tried to figure it out, attempting to rescue Hume from an embarrassing self-contradiction. After all, this is arguably the most influential philosopher ever to write in the English language. Could it be he didn’t notice that he had successfully refuted his own cardinal doctrine, on which his entire philosophical work is based?

In the following we will look at three of several possible solutions to Hume’s blue dilemma, as summarized in a nice paper by John Nelson (published in 1989 in Hume Studies). I will then argue that there is a good chance that Nelson (and others) over-analyzes things, which is typical of, ahem, analytical philosophy. The answer may be much simpler, more satisfying, and more in synch with Hume’s own conception of “moral” philosophy as analogous to natural philosophy (“moral” at the time indicated all of philosophy other than science, not just ethics). And I will accomplish all of this while at the same time showing just how sensible Hume really was!

The first suggestion advanced by Nelson (rather informally, since he says he overheard it from a colleague…) is that Hume deliberately weakened his empiricist position, giving an opening to the rival rationalist approach through a sort of self-created Trojan horse. Admitting that the missing shade of blue could be conceived a priori, i.e. without recourse to experience, would, in fact, do just that. Now, why would Hume shoot himself in his philosophical foot? Because Hume’s philosophy also includes an important role for instincts (which in fact he discusses right after the section we are concerned with here), and instincts are innate, i.e. they precede direct sense experience. Nelson, however, immediately discards this possibility for the explanation of the missing shade’s problem. If that were really Hume’s intent then he would have constructed his subsequent arguments in the Enquiry in a much more rationalist-friendly fashion, which he most certainly didn’t do.

Option two, then. This one comes from R. Cummins, who proposed it back in 1978 (in philosophy things move slowly, as you know). Essentially, the suggestion is that one can reasonably interpret Hume’s “having an idea of X” (say, the missing shade of blue) as meaning “having a capacity to recognize X,” in which case the apparent contradiction would instantly disappear, since Hume wouldn’t be providing an example that potentially undermines his main thesis, he would simply entertain the possibility that people are capable of recognizing that there is a missing shade of blue among a range of colors offered to them. The problem with this “solution,” as Nelson quickly points out, is that Hume himself is very clear that he considers the missing shade to be a “contradictory phenomenon,” which is entirely inconsistent with Cummins’ way out of the dilemma.

What then? Nelson has his own theory, of course. (Are you still with me? I promise, there will be a pay off, coming up shortly…) This one is subtle and clever. Indeed, I think, too subtle and clever. Nelson essentially suggests that Hume’s bringing up of a possible contradiction to his main thesis about how people form ideas (ultimately, from experience) is in perfect harmony with his even more general thesis that human understanding of “matters of facts” (i.e., everything outside of math and logic) is only probable, never certain. You see the twist? Hume, according to Nelson, is providing a (possible) example of how his own theories about a particular matter of fact — the ultimate origin of human ideas — could be mistaken, which proves his meta-point about there being no such thing as certainty about anything empirical. Very clever, very elegant, and very likely an unnecessary overreach on Nelson’s part.

My humble opinion — since I’m not a Hume scholar — is simply that we need to take Hume at his words. Re-read, if you please, the passages by him that I quoted above, and pay particular attention to the italicized parts: “it is not absolutely impossible,” “simple ideas are not always, in every instance,” “this instance is so singular, that it is scarcely worth our observing,” “does not merit that for it alone we should alter our general maxim.”

Did you see it? Hume simply found a hypothetical example (it would actually be very difficult to do the experiment, if you think about it) that doesn’t go well with his general account. But he thinks that the alleged exception is so contrived as to fail to make a general point, and he therefore (wisely) proceeds to ignore it.

This attitude is similar to the one unreflectively adopted by practicing scientists, and philosophers in general — especially those of the analytic tradition — could benefit from imitating Hume more often. Too many philosophers seem to think that when they find an apparent exception to a general concept, no matter how unlikely or artificial, they have “defeated” the general notion, that exotic counter-examples provide knock-out arguments against a given thesis. But in reality this is generally not the case, and philosophers should just relax about it.

For instance, you may recall my discussion of so-called “Gettier cases” in the context of a treatment of the concept of knowledge. Ever since Plato, knowledge has been defined as justified true belief. Then came Edmund Gettier, who in 1963 published a paper showing that there are instances of what one should consider knowledge and that yet do not seem to agree well with Plato’s definition (read my original post if you are interested in the details). I do consider this an example of (minor) progress in philosophy, because as a result of Gettier-type cases we now have a more nuanced understanding of what counts as knowledge and why. But it can easily be shown that all Gettier-type exceptions to Plato’s concept of knowledge fall into a very narrow category, and they are all very highly contrived. What would a good scientist do, when faced with such narrow anomalies? Very likely precisely what Hume did: ignore them, at least provisionally, and focus instead on the general account to see just how much it can explain before having to be refined or expanded.It should not come as a surprise, then, that the highly sensible David Hume, whose project was precisely to turn “moral” philosophy into something more akin to natural philosophy (i.e., science) would adopt the pragmatic approach that is so effective in the latter practice. If only more contemporary philosophers were more Humean in spirit I think the whole discipline would greatly benefit. As Hume himself put it, when he happened to be temporarily overwhelmed by a hopelessly complex philosophical problem, “I dine, I play a game of back-gammon, I converse, and am merry with my friends; and when after three or four hours’ amusement, I wou’d re turn to these speculations, they appear so cold, and strain’d, and ridiculous, that I cannot find in my heart to enter into them any farther.” Cheers!

I don't fully agree with any of the proposed interpretations, although mine is very close to yours. I think the truth is very simple.

As with your interpretation, I think that Hume brought up the example of the missing shade of blue not to make some grander point or to sneak in a Trojan horse but out of intellectual honesty. In thinking on the matter, his mind came upon this troubling counter-example and he couldn't but include it as to do otherwise would have been dishonest.

I disagree with you on the wisdom of dismissing contrived counter-examples in general. I think contrived scenarios can and do illuminate serious problems with philosophical positions, and we would do well not to ignore them. I think in Hume's case he may have been somewhat justified in dismissing it, as it seems he didn't have a sufficiently rigorous understanding of how the brain modelled colour to draw any firm conclusions, especially when the example is so "singular".

I think had he the benefit of more time to think about it or greater understanding of how human perception works, he might have realised that colour is a compound sensation. Each colour has brightness, hue and saturation (or ultimately red, green and blue). Furthermore, all sensations have an "intensity" component. Any missing shade of blue can therefore be created in the mind by activation of the appropriate representations for brightness hue and saturation with the appropriate intensities. The missing shade is therefore composed of simpler sensations which all have been experienced previously.

If the man had lived his life in a world entirely devoid of blue light, I find it highly improbable that he could imagine any shade of blue at all. I think this makes my interpretation highly plausible.

All that said, I'm not sure I totally buy the larger conclusions Hume is drawing. It is not obvious to me that entirely new ideas cannot be conceived of without drawing on experience, and it is not clear to me that the distinction between thoughts and sensation is as clear as Hume makes out. What he says is plausible, but I'm not 100% convinced.

Simply because he didn't prove it to my satisfaction. His argument is based on assertions and introspection.

I think we are not blank slates. I think we have developed some instincts and basic ability to reason in the course of our evolution that could perhaps take the place of direct personal experience in helping to form thoughts.

It would seem to be a bit limiting to say that an idea is a reflection of ONLY one sensation. Instead might it be better to say an idea is a generalization of sensations? This would allow someone to interpolate between experienced sensations of a similar nature to have an idea that encompass a sensation that we have not directly experienced, but not a type sensation that we have not experienced yet.

I'm a bit confused as to what Humes meant initially with his impressions. Would his view not allow for initial impressions that develop corresponding ideas about the world to later effect new impressions and ideas?

I have some reservations regarding your presentation, Massimo. Most have to do with your choice of wording that seems at times prejudicial, for example, "so contrived" or "unreflectively adopted" or "apparent exception" or "highly sensible David Hume."

To my mind, such usage weakens what seems your point: "...ignore them, at least provisionally, and focus instead on the general account to see just how much it can explain before having to be refined or expanded." This phrasing seems to beg the point, despite your careful insertion of "at least provisionally." The question remains why Hume raised this "singular" instance. What is the basis for deciding what is contrived (like many thought experiments) and how does one reach the point of "provisional" acceptance?

In this regard, I'm with DM. I think he's anticipating counter-arguments and is being intellectually honest in doing so. For this reason, I'm inclined look more favorably upon Nelson's argument. Hume's example does raise the issue of probability and statistical significance. And, on the basis of your description of Nelson's argument, it seems consistent with Hume's thinking. Further, the fact that in the example the person is blind seems irrelevant to me. It is not uncommon for visual artists to mix colors to create one that serves their purpose, regardless of whether they've previously "experienced" the shade. (Think of Titian "red" and the confusion with "Venetian" red or auburn. Neither of which can be said to "qualify" as Titian.)

All very well, but Hume would have had an easy solution available, and I wonder why he did not employ it: The idea of this shade of blue could be seen as akin to those "combinations of simpler ideas" or, in Jesse Huebsch's words, could be arrived at through interpolation, because the person has seen enough other blues around it that we do not need to see that particular blue as a completely new, independent sensation.

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When I read things like this:

Ideas are thoughts, while impressions are sensations. The first are derived from memory and abstract thinking, the second from the senses. Ideas, Hume argues, are (weaker) “copies” of impressions, and impressions are obtained directly from experience. For instance, we can feel love for someone (an impression) and we can think about the concept of love (an idea). Clearly, says Hume, the feeling is much stronger than the concept, as expected if it were derivative. Ultimately, according to Hume, all knowledge comes from experience

... I wonder immediately, "how do you know"? Yes, Hume presents arguments, but the question is really an empirical one. This is a rare case where neuroscience might actually be useful for something.

Durland "Hume's First Principle, His Missing Shade, and His Distinctions of Reason" (1996) points to Hume's later comment:

"...evident that even different simple ideas may have a similarity or resemblance to each other; nor is it necessary, that the point or circumstance of resemblance shou’d be distinct or separable from that in which they differ. Blue and green are different simple ideas, but are more resembling that blue and scarlet; tho’ their perfect simplicity excludes all possibility of separation or distinction.’Tis thesame case with particular sounds, and tastes and smells."

and concludes that "such partial resemblances are possible only if the perceptions themselves have distinguishable aspects, Hume is committed to the view that simple impressions have distinguishable features". That is, the gap in a series of shades of blue is recognized via "a distinction of reason", a recognition that there is a perceptual colour space.

Alex, your statement, "The idea of this shade of blue could be seen as akin to those "combinations of simpler ideas" or, in Jesse Huebsch's words, could be arrived at through interpolation" is true. DM suggested the same in his comment.

Of course, Hume could have said the same, but apparently didn't. At least not in the quote Massimo provided. So, I don't find it a satisfactory explanation. Is this how it worked for Titian: "I need a shade of red in my painting, but I have no idea what it is until I mix together some colors that approximate those I've seen (experienced) in the natural world" ?

It strikes me that much of the human endeavor, once the basics are taken care of (I'm thinking of you, Maslow's hierarchy), is to figure out how to make the highly improbable, probable enough to be detected. If our efforts to build a higher structure fail, let's find better building blocks or methods of connectivity. If our supercolliders can't accelerate particles to high enough energies, let's build bigger ones until we can discover e.g. the Higgs boson. To spite Hume, the human endeavor is to become a miracle-worker. :-p

Bringing this closer to this blog post, consider the New Yorker article "Why Smart People are Stupid" [1], which makes the audacious claim (at least according to the person who sent me the article) that it is not possible to overcome one's cognitive biases. Perhaps Jesus was giving us the impossible task when he said to first take the log out of our own eye, before removing the speck from the eye of the guy who is so clearly wrong. This might be a stretch, but I wonder if Hume set limits on what human cognition might be capable of in how he spoke. I'm getting whiffs of Aristotle's biological teleology, and how it probably set science back for centuries.

I want to acknowledge and thank David Duffy for his comment. I didn't see it before my previous comment. Nevertheless, I still don't find this satisfying. I wonder if Hume ever addressed delusional thinking. And I can help thinking we are knocking on the door of a slightly different version of Mary's Room. I realize I may be drifting a bit from the major point in Massimo's post, though.

Massimo, this reminds me of what Hume allegedly said when asked if he worried about issues presented by the problem of induction or other issues in his philosophy,m and he simply said, in effect, "Nope, I just go to sleep at night."

> I disagree with you on the wisdom of dismissing contrived counter-examples in general. I think contrived scenarios can and do illuminate serious problems with philosophical positions, and we would do well not to ignore them. <

I don’t think counter-examples should be dismissed in general, but I do feel like too often they are given undue attention, especially when they are obviously contrived. I think the attitude stems from an archaic approach to philosophy, rooted in classical logic: given sharp concept and definitions, then a single exception changes everything. But most interesting concepts in both science and philosophy are not like that. They are somewhat fuzzy and admit of exceptions. The exceptions may be interesting (like Gettier cases), but not as crucial as some people seem to think.

> The missing shade is therefore composed of simpler sensations which all have been experienced previously. <

I’m not so sure. This may stretch the definition of “based on simpler sensations,” but maybe you are correct. Anyone who knows more about color perception wants to chime in?

> It is not obvious to me that entirely new ideas cannot be conceived of without drawing on experience <

It isn’t entirely clear to me either. I was simply summarizing Hume’s views, not mine.

Jesse,

> Instead might it be better to say an idea is a generalization of sensations? This would allow someone to interpolate between experienced sensations of a similar nature to have an idea that encompass a sensation that we have not directly experienced <

> Would his view not allow for initial impressions that develop corresponding ideas about the world to later effect new impressions and ideas? <

Yes, but that would still mean that ideas are only combinations or variations of impressions, not anything entirely new (like, allegedly, the missing shade of blue).

Alex,

> The idea of this shade of blue could be seen as akin to those "combinations of simpler ideas" or, in Jesse Huebsch's words, could be arrived at through interpolation <

Not quite that simple, actually. Is interpolation a combination of already existing ideas, or does it require a novel contribution of thought? If the latter, that avenue would have been precluded to Hume.

> Hume presents arguments, but the question is really an empirical one. This is a rare case where neuroscience might actually be useful for something <

Indeed, which is perfectly in synch with Hume’s approach. He was convinced that “moral” philosophy needs to take a hint or two from natural philosophy. That was the crucial idea behind his entire program.

David,

> That is, the gap in a series of shades of blue is recognized via "a distinction of reason", a recognition that there is a perceptual colour space <

> This might be a stretch, but I wonder if Hume set limits on what human cognition might be capable of in how he spoke <

The recognition of human epistemic limits was a central part of Hume’s quest, but I wouldn’t say that he “set” limits, he was interesting in openly inquire about their extent.

Thomas,

> I have some reservations regarding your presentation, Massimo. Most have to do with your choice of wording that seems at times prejudicial <

This is a blog, which means it’s a collection of op-ed pieces, so it’s not at all strange that my opinions come across loud and clear, and I don’t apologize for it.

> What is the basis for deciding what is contrived (like many thought experiments) and how does one reach the point of "provisional" acceptance? <

Good question, and my guess is that the answer varies from one case to another. I consider Gettier cases about knowledge contrived, for instance (so do many people who work in that area, by the way, even those who find them interesting).

> I think he's anticipating counter-arguments and is being intellectually honest in doing so <

I wish people took a breadth (or two, or three) before implying that their interlocutors are being intellectually dishonest. And incidentally, what can be more *honest* than to wear one’s opinions on one’s sleeve?

> It is not uncommon for visual artists to mix colors to create one that serves their purpose, regardless of whether they've previously "experienced" the shade <

But that’s not really relevant to Hume’s point: artists may be capable of mixing colors they can’t perceive, but the question is about their perceptions, not their manual (or artistic) abilities.

> Is this how it worked for Titian: "I need a shade of red in my painting, but I have no idea what it is until I mix together some colors that approximate those I've seen (experienced) in the natural world"? <

Actually, that quote seems to go right along with Hume’s contention that one *cannot* imagine shades of color he hasn’t seen. Not even a great artist like Titian!

> I can help thinking we are knocking on the door of a slightly different version of Mary's Room. <

Yes, I had the same thought too.

Gadfly,

> this reminds me of what Hume allegedly said when asked if he worried about issues presented by the problem of induction or other issues in his philosophy,m and he simply said, in effect, "Nope, I just go to sleep at night.” <

He was a great man, and a great philosopher.

Mark,

> Given that we have so much more knowledge of the scientific questions than they did, I would suggest that their (from our perspective scientifically ignorant) reflections are of limited value. <

You should read Dennett’s chapter, in his latest book, on why philosophers still study the history of their own field — and why scientists should do the same. But yes, of course the specific empirical points made by past thinkers become less and less relevant. It is the conceptual points that may still require our attention, and Hume provided a good number of them, which is why he is still so relevant today.

Massimo, after I wrote my initial post (and, tho not a professional philosopher or a Hume scholar, I've read much of what he's written, and very much agree — he could be considered the first modern psychologist, among other things), I got to thinking further ...

What if this is even more than a "throwaway," and rather, a deliberate straw man? He sets up this incredibly hypothetical example to say, "See, this is the best counterexample possible to my ideas."

I think that Hume's dismissal of the missing shade of blue can be justified, *but* I also think Hume owed us a better explanation himself and shouldn't have dismissed it so cavalierly. Sometimes small counterexamples to general principles isolated in a highly controlled lab environment are the key to uncovering deeper counterexamples, more systematic counterexamples.

The reason why I think Hume owed us a better explanation of his treatment of the counterexample is due to how he treats the idea of causation. Hume has to bend over backwards to make the idea of causation conform to his copy principle because he is so reluctant to admit a further counterexample to it. He even recognizes that his conclusions about causation are wildly counterintuitive ("I doubt not but my sentiments will be treated by many as extravagant and ridiculous...a gross absurdity, and contrary to the most certain principles of human reason", p. 167).

Hume's opponents could reasonably say: "Hey, Hume, rather than accepting your wildly extravagant conclusions, maybe it would be more plausible to suppose that the idea of causation is a counterexample to your copy principle. You yourself admitted that there can be counterexamples in some rare and contrived cases. Why not think we've stumbled across a common, non-contrived counterexample?"

Now, I think there are a couple of responses Hume could have given:

1) Hume could have said that what he was really trying to do was to show that there are no 'pure intellectual' ideas, and that all ideas are basically represented in the imagination (i.e.: all ideas are basically 'mental images' - something a rationalist like Descartes would emphatically deny.) Although the missing shade of blue counterexample violates the impressions-before-ideas principle, it *doesn't* violate the more general principle that all ideas are basically just faint mental images (or 'weak impressions'). It turns out that this latter principle is really what Hume needs for most of his arguments to work.

2) Causal beliefs and inferences are an extremely robust phenomenon (unlike the missing shade of blue) - Hume thinks they happen basically the same way in adults, young children, smart people, stupid people, and even in animals (he talks about this in the section 16 of the treatise), and they happen in all kinds of situations. So Hume thinks that a plausible, unified account of this widespread psychological phenomenon must depend only on simple operations of the mind common to the smart, stupid, young, old, animals, etc. His account of causal belief/inference provides such an explanation. He thinks that alternative explanations that violate the copy principle necessarily invoke some overly intellectual faculty that wouldn't plausibly be found in young children or animals. Long story short, Hume isn't applying some kind of arbitrary double standard when he sticks to the copy principle in the case of causation but not in the case of the missing shade of blue.

I love your point about counter-examples, Massimo, and I think it can be generalized to many a "thought experiment" which, after all, is exactly what this is. I guess figuring out which counter examples are worthy is what Daniel Dennett is all about. And I think you are right that the undue attention comes from extending logical rigors to areas where they don't apply, especially areas that are so empirical. But if Hume is raising the issue and then shrugging it off, isn't that what most of us do with Hume's ideas about induction? They can't be defeated, but they, like other unbeatable skeptical stances (naive solipsism, idealism) also can't really be taken onboard, not if you want to have a career in science and the world as it really, really is.

> The idea of this shade of blue could be seen as akin to those "combinations of simpler ideas" or, in Jesse Huebsch's words, could be arrived at through interpolation <

Massimo

Aren't we really just talking about creativity here, and isn't this a hallmark of human cognition? We have the capacity to place things outside of their commonly perceived associations such as applying a tool generally used for a specific task to a novel application. Isn't this also in sense what all philosophers do?

Don't they draw on common or prior accepted perceptions/conceptions and create a novel presentation that re-frames how we might conceive of things. I would argue that when this is successful it can also feedback to a degree upon how we perceive the world.

I would certainly agree that many of our impressions (perceptions) occur through unconscious mechanisms, but did Hume rule out a feedback role for our rationality or beliefs in this process? In other words did he only see the relationship in one direction impressions->beliefs with no role for beliefs->impressions?

He definitely allows for that - he calls them 'secondary impressions' (and 'secondary ideas'). They usually involve emotions or 'passions' (which Hume considers to be a kind of impressions). For example, merely thinking about an idea can give rise to strong emotions.

Unless those 'secondary impressions' are limited only to already experienced 'impressions' than this seems to imply that we might be able create novel 'impressions'. Thinking about an idea might give rise to strong emotions, but it also might lead to a more nuanced or subtle emotion in response to a previously familiar context that in the past produced a strong emotion.

It should be noted that whether we create novel impressions isn't really an issue for Hume. Hume actually says that the source of impressions is unknown - sometimes he doesn't even seem to think there's an external world that causes impressions. Hume's main concern is that (simple) ideas are copied from (simple) impressions - where those impressions come from isn't of much importance to him.

Massimo: "This is a blog, which means it’s a collection of op-ed pieces, so it’s not at all strange that my opinions come across loud and clear, and I don’t apologize for it."

Yep. And I've said the same about your right in this regard on other posts. I don't expect an apology. I made an observation about your choice of wording. As I said, "To my mind, such usage weakens what seems your point . . . ." No offence was intended.

Massimo: "I wish people took a breadth (or two, or three) before implying that their interlocutors are being intellectually dishonest. And incidentally, what can be more *honest* than to wear one’s opinions on one’s sleeve?"

I don't really know what to make of this. My comment wasn't meant to imply that an interlocutor was being intellectually dishonest. The question, as I interpreted it, was why did Hume include the shade of blue argument. I suggested that he was being intellectually honest by including it. Perhaps, it was an argument a friend raised while they were discussing his "general maxim" over a cup of tea and Hume decided to include it and then dismiss it as a matter of no great consequence. This amounts to nothing more than speculation about his motivation. I happen to like Nelson's speculation. As you put it, "Hume, according to Nelson, is providing a (possible) example of how his own theories about a particular matter of fact — the ultimate origin of human ideas — could be mistaken, which proves his meta-point about there being no such thing as certainty about anything empirical." You may think this over the top, but it is no more so someone speculating that he included it as a private joke amongst friends.

Massimo: [two separate comments]

1. "But that’s not really relevant to Hume’s point: artists may be capable of mixing colors they can’t perceive, but the question is about their perceptions, not their manual (or artistic) abilities."

2. "Actually, that quote seems to go right along with Hume’s contention that one *cannot* imagine shades of color he hasn’t seen. Not even a great artist like Titian!"

I strayed from the main point of your post, I think. Still, in my opinion (1) No and (2) No. I simply have a problem with Hume's contention, as you put it, "Ideas . . . are (weaker) 'copies' of impressions . . . ." In what way can it be said that Titian's "Venus and Adonis" or Van Gogh's "Starry Night" is a copy--weak or otherwise--of impressions? Or for that matter, Shakespeare's "Macbeth"? Further, I might suggest that the "copies of impressions" in this context is not subject to empirical analysis, but is rather flirting with a value judgement. Sure, it appears that Hume makes room for imagination and instinct and distinctions of reason. But this, to me, is hedging, honestly allowing some wiggle room for himself and his maxim. "That stick is 12 inches long." What sense impression of the stick led to the idea to measure the stick? If Hume is saying that the idea of a 12 inch stick is not identical to the stick, excuse me if I shrug and walk away.

Returning to what seems to me to be the point of your post, I would describe it as the "chicken little" metaphor. No the sky isn't necessarily falling. But who gets to characterize the exception as "chicken little" stuff?

>> In what way can it be said that Titian's "Venus and Adonis" or Van Gogh's "Starry Night" is a copy--weak or otherwise--of impressions? Or for that matter, Shakespeare's "Macbeth"?

Strictly speaking, Hume's copy principle says that only *simple* ideas need to be copies of (simple) impressions. The mind is free to create new brand new complex ideas by mixing and matching the simple ideas in whichever way it pleases - for example, he says that people can have ideas of cities made entirely from gold (even though nobody has ever had an impression of such a city). So I don't see how those examples you give pose a challenge for Hume. Nor do I see why this is "hedging" - it's all a part of his system (a system he has largely borrowed from earlier empiricists, such as Locke and Hobbes).

>>What sense impression of the stick led to the idea to measure the stick? If Hume is saying that the idea of a 12 inch stick is not identical to the stick, excuse me if I shrug and walk away.

I don't really understand what you're saying here. Are you saying that we have a general idea of "12 inch stick" that is distinct from our ideas of this particular stick or that particular stick? Hume argues (following Berkeley) that we don't have general ideas of that sort (this is one of his main points of disagreement with Locke). Obviously you don't have to agree with Hume - I'm just pointing out that these are all things he considered.

It seems we have a fundamental way of conceiving of distance or proximity regardless of whether the context involves space or time or a social situation which to me with it's global application feels more like an impression or perception than an idea. The article somewhat paradoxically describes this 'sense' as allowing us to abstract or move beyond experience.

C, I appreciate your taking the time to comment. I'm simply rejecting what has been presented in this post to suggest that (human) ideas/thoughts can be simply described as copies or "partial resemblances" (whatever that conveys, though I assume we could try to measure a resemblance in terms of degree). The works of art I mentioned are not reducible to me in terms of sensory impressions. In fact, they are not copies per se. Other animals have sensory impressions. Where are their copies? So, I find the notion that ideas/thoughts are copies of impressions to be inadequate in this regard. Let's say I have three sticks of varying lengths that I toss while asking my Cairn Terrier to fetch and return the one that is 12 inches long. I may not be totally surprised if he selects the correct one, but I doubt that I could adequately claim this was due to the copy of a 12 inch long stick that he had formed on the basis of his sensory impressions.

>>C, I appreciate your taking the time to comment. I'm simply rejecting what has been presented in this post to suggest that (human) ideas/thoughts can be simply described as copies or "partial resemblances"

I would be surprised if *anybody* in this discussion agreed with Hume on this point. In fact, I would be surprised if anybody here accepted Hume's entire impression/idea framework. That was not the point of Massimo's post. So I'm not trying to convince you that Hume was right on this matter. However, your objects seem to betray misunderstandings of what Hume says.

>>The works of art I mentioned are not reducible to me in terms of sensory impressions. In fact, they are not copies per se.

I don't know how to make sense of this. Hume is making a claim about the relation between impressions and ideas - two different kinds of mental representations. Pieces of art are not mental representations - they're physical objects (well, at least in the case of paintings). So I have no idea what it would mean to say "a piece of art is (or isn't) reducible to sensory impressions" - unless perhaps you're an idealist who thinks everything in the world is made of ideas.

The closest thing I can think of that you might be saying is something like this: When somebody looks at a painting (such as "Starry Night"), he experiences a visual impression of the painting. But the corresponding idea that he develops of the painting contains more 'information' or 'content' than was contained in the initial visual impression. If you have something like that in mind, that's an interesting claim. Otherwise, I have no idea how it bears on what Hume says.

>> Other animals have sensory impressions. Where are their copies?

In their minds. That's where ideas (and impressions) are generally located. The question "Where are the copies of the dog's impressions?" should be no more mysterious to you than the question, "Where are the copies of Barack Obama's impressions?"

>>Let's say I have three sticks of varying lengths that I toss while asking my Cairn Terrier to fetch and return the one that is 12 inches long. I may not be totally surprised if he selects the correct one, but I doubt that I could adequately claim this was due to the copy of a 12 inch long stick that he had formed on the basis of his sensory impressions.

Again, your point seems to betray a misunderstanding of Hume. He doesn't say anything about copies of 12 inch long sticks. In general, he doesn't say anything about copies of physical objects. The only copies he talks about are ideas being faint copies of sensory impressions. So what is it exactly that you doubt? You doubt that the dog retains a faint copy of his impression of the stick when he stops looking at it?

C, thanks again. First, I'm going to concede what is obvious: That most of the commentators are much more familiar with Hume than I am. Second, I'm going to restate that I strayed from the Massimo's central point of the post.

I have already indicated that I find the notion, as stated in the post, that Hume believed idea/thoughts are copies of sensory impressions to be inadequate and unsatisfying. Hume himself points to this in his shade of blue example. He just doesn't think the example is sufficiently strong to counter his general maxim.

You are close to describing my objection with the Titian and other examples when you write:

"The closest thing I can think of that you might be saying is something like this: When somebody looks at a painting (such as "Starry Night"), he experiences a visual impression of the painting. But the corresponding idea that he develops of the painting contains more 'information' or 'content' than was contained in the initial visual impression. If you have something like that in mind, that's an interesting claim. Otherwise, I have no idea how it bears on what Hume says."

Yes,except that I am less concerned with what a viewer's impressions of the finished work are than I am with the actual process and many decisions made by the artist in creating the work that cannot only be said to copy sensory impressions. The point of the 12 inch stick is not that there is a 12 inch stick, but that somebody decided to measure it. Surely the decision to measure is an idea. But in what sense is this decision to measure a copy of sensory impressions?

Actually, Hume would describe the decision to measure as a kind of impression (specifically, it's a "volition"). Impressions for Hume aren't limited to sense perceptions - they also include emotions, desires, and the feeling of 'willing' something to happen. Hume has to put together a bunch of complicated machinery to explain where and how a volition comes about. Again, I'm not saying I agree with Hume - I'm just pointing out how he tries to account for these things.

You're simply trying to defend what is ultimately indefensible, because Hume is one of your intellectual heroes. The "missing shade of blue" refutes his thesis that all our ideas are ultimately derived from sensory impressions (your objections to the contrary notwithstanding). And this is not the only "anomaly." There are others and more prominent ones. Clearly, math and logic are not derived from sensory impressions.

I am not sure why you are suggesting that this is the way science is done. I can hardly imagine Planck going off to eat, play backgammon and have fun with his friends and then saying that he hadn't the heart to go into it further and that we should not let the ultraviolet catastrophe alter the general idea of Raleigh-Jeans.

I just re-read that section and here is another exception that Hume mentions and then discards:

"But, except the mind be disordered by disease or madness, they never can arrive at such a pitch of vivacity, as to render these perceptions altogether undistinguishable."

Why ignore the exception? Surely this is an important point to consider? Is there an actual distinction between impressions and ideas? Could there be an impression unless we had an idea of what the impression was of?

>>So we take the term 'idea' and ask "from what impression is that supposed idea derived?"...It would then seem that we should banish 'idea' as jargon and so reject the argument.

Hume would say that "idea" is a general term that applies to a class of ideas (in particular, all of them). It is really no different from his treatment of other general terms, such as "triangle" (a term which applies to a whole class of ideas about particular triangles). So to the extent that Hume can adequately treat general terms at all, Hume has no problem talking about "ideas" and "impressions."

>>Why ignore the exception? Surely this is an important point to consider? Is there an actual distinction between impressions and ideas?

This is actually a vexed question for Hume scholars. Personally, I think it's a pretty serious problem for Hume.

I love reading Hume and I think he had great ideas, but I honestly think he was a rather fast-and-loose philosopher. The passage you quoted is just one of many examples of that.

>>Could there be an impression unless we had an idea of what the impression was of?

Well, in the case of *current* impressions, Hume thinks the impressions are automatically copied as faint ideas. So in the case of current impressions, the answer to your question would be "no": whenever you have an impression of something, you'll also have the corresponding idea of it.

However, it's possible to have experienced an impression *in the past* but not retain the corresponding idea. For example, I no longer remember exactly what my great grandmother's face looked like. I experienced an impression of her face at some point in the past, but I no longer have a corresponding idea of her face.

But I think a current impression is also an idea. I remember my Mum telling me that once, when she was unwell and tired, she looked out the window and saw a man feeding his dinosaur.

In the very next instant, realising that this could not be true, she concluded it was someone standing next to a digger and looked out the window and saw that this was in fact the case.

It is a little contrived due to her being unwell but it is an example of a current impression which is a wrong idea and replaced immediately be an idea which is true to what was happening.

So I think that our current impressions, as soon as we are aware of them, are ideas in pretty much the same way as a memory of it except that we are getting more confirmations from continuous sense data.

C February wrote : "Hume would say that "idea" is a general term that applies to a class of ideas (in particular, all of them). It is really no different from his treatment of other general terms, such as "triangle" (a term which applies to a whole class of ideas about particular triangles). So to the extent that Hume can adequately treat general terms at all, Hume has no problem talking about "ideas" and "impressions." "<<

I am not sure you understood what I said. If Hume can talk of ideas without subjecting them to the test he, himself, sets for terms then what is the basis for this exception?

Are we to accept his argument even though it is based onterminology fails the test which he says is consequent on that very argument?

I understood your point perfectly, and I was showing you why the word "idea" is *not* an exception to his rule. Let me spell it out more explicitly. Hume writes:

"When we entertain...any suspicion that a philosophical term is employed without any meaning or idea...we need but enquire, from what impression is that supposed idea derived?"

So, for example, if the term in question was 'necessary connection', the question would be: from what impression is the supposed *idea of a necessary connection* derived?

Let's ask the same question for the term 'idea of blue'. So the relevant question would be: from what impression is the *idea of an idea of blue* derived?

Now, Hume actually says that we can have ideas of ideas - they are, as you'd imagine, just faint copies of ideas, which are in turn copies of impressions. So my idea of my idea of blue is derived from my idea of blue, which is derived from an impression of blue. Problem solved.

What about the more general term 'idea'? Now the question becomes: from what impression is my *idea of an idea* derived? In this case, Hume would actually tell the same exact story he told in the previous case. The reason for this has to do with how Hume treats general terms, which I tried to explain in my earlier post. It's not necessary to understand the details of that story. The main point is that, if you were satisfied by the answer I gave for the term 'idea of blue', then Hume would give the same answer for the more generic term 'idea.'

>>It is a little contrived due to her being unwell but it is an example of a current impression which is a wrong idea and replaced immediately be an idea which is true to what was happening.

I think Hume would simply cash this out in different terms. For example, he might say that your mum had some impression of a big brown thing which she *associated* with one idea (the idea of a dinosaur), and subsequently associated with another (the idea of a digger). Alternatively, if your mum's visual impression actually *changed* from one moment to the next, that would just show that she had one impression (and corresponding idea) at one moment, and another impression (and corresponding idea) the next. I don't see why you would say the impression is also an idea.

In any case, I don't think Hume's theory of impressions/ideas is actually true, so we're basically just speculating about how a fictional story would work - like talking about how The Force works in Star Wars

The Gettier cases illustrate the problem, they cannot be dismissed as contrived because surely most misunderstandings in the world happen because of Gettier style beliefs.

If someone believes one proposition on the basis of another false proposition we cannot say that this is not a problem if the first proposition happens to be true.

This will only lead to people putting spurious confidence in the false proposition and then using it to derive many more false propositions.

Better then to find a better definition. In any case I think Gettier's paper is based on a misunderstanding of what Plato meant.

The proposition "I see a barn front" does not justify the proposition "I see a barn" in a country full of fake barns. The proposition "A owns a Ford and either A owns a Ford or is in Barcelona" does not justify the proposition "A is in Barcelona" unless there is some other fact that makes this so.

So what Plato probably meant was something like "A knows P iff there is a true proposition Q which justifies P and A believes Q and that it justifies P".

In fact epistemologists appear to have gone out of their way to say that something that appears to be a justification is, in fact, a justification.

If we are to make progress then obviously we have to think a little harder about what is an actual justification rather than what appears to be justification.

Let me clarify that in Gettier cases one is still believing on the basis of a false proposition because even though the proposition itself may be true, the proposition that it justifies the belief in question is false.

I'm inclined to agree with you Robin. I don't see the Gettier cases as particularly troubling, not because they are contrived but because they are consistent with "justified true belief" if we take "justified" to mean that the premises on which the justification is based are essentially correct.

I've seen Hume referred to as the first 'object modeler' (in the sense of object-oriented programming) with his view that every thing is just a bundle of properties. Maybe he could have used OOP to solve his 'missing shade of blue' problem.

I sent this post to my brother, who is currently doing a post-doc at York, and last year finished his PhD in Cognitive Psychology from Rutgers (with his dissertation being on visual perception); he had this to say:

If someone did not have experience with a single shade of blue they would definitely be able to think about it. The way our color system works is by representing a point in 3D space (roughly Red, Green, and Blue at the retinal level, and possible Hue, Saturation, and Luminance further along in the cortex). It understands that these are continuous variables, and so it would know that if there is a point in that space that it has not encountered before that it is a possible combination of the three variables. For example, if I look at a bunch of data on a scatter plot in (x,y) space. If I never see the point (5,2.4314363723652452) but I have seen (5,2.5) and (5,2.35), I would not think that the point (5,2.4314363723652452) doesn't exist, just that it is a valid point that could occur I simply have not encountered it before, and so I would be able to conceive of that point and have the idea of it without ever having the impression of it (using the words of the post).

There is an experiment done on bees to see if they can extrapolate what they learn, or if they are simple stimulus-response creatures. Bees navigate relative to the sun, but the sun moves throughout the day, so the must understand where the sun could be in the morning if they want to find the flowers that they saw in the evening. Also, bees are able to communicate to other bees where honey is located. In the experiment they only allowed bees to have exposure to the sun in a small period of the day in the morning. They learned how to get from home to the flower. They then told other bees where the flower was (these other bees had been exposed to sun at the same time of the day, but did not learn the location of the flower). These bees were released in the evening and were able to find the flower. This suggests that the bees do not only learn the locations of the sun that they say [to other bees - me], but they can incorporate that the sun moves. Also, if the sun moved up and to the right in the morning, they could extrapolate that the sun always moves up and to the right (meaning in the evening it would be even further up and to the right) but they do not do this. They have some sort of mechanism that lets them know that the sun goes around and doesn't simply continue on in the same direction.

Examples like this bee one are one of the reasons that the nativist/rationalist view is so prevalent in cognitive science (think Pinker or Chomsky - Fodor too, but I would rather not think about him since he is a nut), and helped lead to the cognitive revolution. It seems that the empiricist/associationist view is still commonly held by behavioral neuroscientists, and I think could use a schooling by some of the cognitive neuroscientists which would help reform the field for the better.

But it seems like some people want to dismiss the lost blue example because it is contrived. It is contrived examples (visual illusions) that have led to some big discoveries in vision science because it lets us know the bounds of our visual system and it sheds light on different types of assumptions that are made by the visual system. So I do think examples like this are useful.

> But if Hume is raising the issue and then shrugging it off, isn't that what most of us do with Hume's ideas about induction? They can't be defeated, but they, like other unbeatable skeptical stances (naive solipsism, idealism) also can't really be taken onboard <

Very good point, but there is a difference, I think. The shade of blue example is meant to counter an empirical doctrine, while discussions on induction are about logic. Also, I think what you suggest is precisely what Hume himself did: of course if you want to to science, or even simply function in everyday life, you have to ignore the problem of induction. But you should remember it any time you get too cocky about the powers of reason and science…

Gadfly,

> What if this is even more than a "throwaway," and rather, a deliberate straw man? He sets up this incredibly hypothetical example to say, "See, this is the best counterexample possible to my ideas.” <

Possible, but I doubt it. Doesn’t go with anything I know of, and read by, Hume. He was a shining example of intellectual honesty, and what you suggest is a bit dishonest…

Seth,

> Aren't we really just talking about creativity here, and isn't this a hallmark of human cognition? <

Not really. We are talking about the limits of human inference.

> In other words did he only see the relationship in one direction impressions->beliefs with no role for beliefs->impressions? <

Good question. Probably not, it took Kant for that…

C,

> Sometimes small counterexamples to general principles isolated in a highly controlled lab environment are the key to uncovering deeper counterexamples, more systematic counterexamples <

Sometimes. And sometimes they are intellectually sterile exercises in nitpicking. As Dennett remarked several times, it is a delicate art to distinguish the two.

> Although the missing shade of blue counterexample violates the impressions-before-ideas principle, it *doesn't* violate the more general principle that all ideas are basically just faint mental images (or 'weak impressions'). It turns out that this latter principle is really what Hume needs for most of his arguments to work. <

No, I don’t think Hume would have been happy with that, since he was an empiricist. All mental images eventually have to trace back to impressions, if one has to avoid the rationalist position.

Thomas,

> As I said, "To my mind, such usage weakens what seems your point . . . ." No offence was intended <

None was taken, thank you.

> I don't really know what to make of this. My comment wasn't meant to imply that an interlocutor was being intellectually dishonest. <

> In what way can it be said that Titian's "Venus and Adonis" or Van Gogh's "Starry Night" is a copy--weak or otherwise--of impressions? <

They are neither. They are works of art which generate both impressions (when you see them) and ideas (when you think about them). And of course Hume would likely argue that the works themselves are the result of combinations of impressions and ideas in their authors’ minds, none of which seems to me to present a problem for his account (which I don’t actually buy, by the way — see below my response to Alastair).

> If Hume is saying that the idea of a 12 inch stick is not identical to the stick, excuse me if I shrug and walk away <

> You're simply trying to defend what is ultimately indefensible, because Hume is one of your intellectual heroes. <

While the latter is true, the first one is false and — I think — a willful misunderstanding of my post. I am not an empiricist in the sense of Hume, and therefore I couldn’t possibly try to defend the indefensible. I agree with Kant on this (who was famously “awakened from his slumber” by reading Hume), that we come equipped with built-in knowledge about things like space, time, causality and even certain basic aspects of the behavior of physical and biological objects. Kant wrote before Darwin, but nowadays it is pretty uncontroversial that we get this innate knowledge by genetics and past natural selection, just like plenty of other species.

> Clearly, math and logic are not derived from sensory impressions. <

And there goes another big thing you missed. Yes, and Hume obviously knew this. Which is why he made a distinction between “matters of fact” and “relations of ideas.” The latter, which include logical and mathematical relations, can be apprehended by the mind without having to be copied from sense experience.

Robin,

> I am not sure why you are suggesting that this is the way science is done. I can hardly imagine Planck going off to eat, play backgammon and have fun with his friends <

Well, too bad for Planck, I’d say! My comment was simply that scientists tend to be much less picky about anomalies in their theories (as Kuhn rightly observed), and for good reasons: theories (scientific or otherwise), especially early on, are very much works in progress, and if we abandoned them at the whiff of an inconsistency we would never get our understanding off the ground.

> "But, except the mind be disordered by disease or madness, they never can arrive at such a pitch of vivacity, as to render these perceptions altogether undistinguishable.” Why ignore the exception? Surely this is an important point to consider? <

Because disease and madness tell us a different story, not one about how the human mind normally works, which was Hume’s intent. It is clearly dysfunctional to have a mind that doesn’t allow you to make a distinction between reality and dreams, isn’t it?

> So we take the term 'idea' and ask "from what impression is that supposed idea derived?” <

Interesting point, and I suppose Kant thought about that sort of thing when he was awakened by Hume. However, don’t forget that this whole discussion is about human understanding of “matters of fact.” As I mentioned above, Hume had different, ahem, ideas about how we reason concerning “relations of ideas.”

> The Gettier cases illustrate the problem, they cannot be dismissed as contrived because surely most misunderstandings in the world happen because of Gettier style beliefs. <

I didn’t mean to dismiss them, as a reading of my post on Gettier cases should make clear. I did mean, however, to cut them down to size a bit, as I think they deserve to be, for the reasons I have explained.

> In any case I think Gettier's paper is based on a misunderstanding of what Plato meant. <

That’s news to me, and to a bunch of people who have spent considerable energy on both Plato and Gettier.

> what Plato probably meant <

I’m no Plato scholar, but I never heard a Plato scholar argue that, so I’m skeptical.

I would be interested to read the thinking of a Plato scholar on this, but one thing is certain - Plato explicitly brings up the case of a belief being true by accident. Also, it seems to me that Plato is saying that the justification must be specific to what it is justifying - differentiating it from other things.

For example I think we could take the false barn example and show how the justification for believing that they have seen a barn does not meet the criterion Plato sets because in a county of false barn fronts the front of a barn is not a distinguishing feature.

But if I recall correctly Plato never puts any definite conclusion on it himself - he seems to do what you say Hume is doing and admitting to anomalies while not rejecting the entire proposition because of them.

> "Ever since Plato, knowledge has been defined as justified true belief.” This is not even close to correct. The entire Aristotelian tradition is a counterexample <

I don’t think so, and — again — never heard a serious student of epistemology claim as much. Would care to elaborate?

Borednihilist,

thanks for reporting the feedback from your brother. He is certainly right about bees’ (and humans’!) ability to extrapolate, and as I said above, I don’t actually buy Hume’s account, ultimately.

I’m less convinced by his explanation of color perception as a function of coordinates. That may be a good way in which cognitive scientists can represent what’s going on, but does the human mind work that way? That was Hume’s question.

It's not clear that what Borednihilist's brother said conflicts with Hume. Unfortunately, Massimo skipped over this key part of the missing shade of blue passage:

" ’tis plain, that he will perceive a blank, where that shade is wanting, and will be sensible, that there is a greater distance in that place betwixt the continguous colours, than in any other."

So Hume CLEARLY admits that the subject of the experiment understands that there's a 'gap' in the shades of blue he has been presented with. And he could coherently think and talk about 'the missing shade' that would fill in that gap. This all seems consistent with what your brother said.

What Hume is asking is whether the subject of the experiment can close his eyes and literally *visualize* exactly what that missing shade of blue would look like. Understanding that the missing shade is a bit lighter than shade X and a bit darker than shade Y isn't quite the same as actually picturing the shade in one's imagination. To use a rough analogy, if I try to imagine what my sister and her husband's children will look like someday, I understand abstractly that they'll probably look like some kind of cross between my sister and her husband, but it's really difficult for me to close my eyes and visualize what that would look like.

>>No, I don’t think Hume would have been happy with that, since he was an empiricist. All mental images eventually have to trace back to impressions, if one has to avoid the rationalist position.

It depends on what you mean by 'rationalist position.' A key part of rationalism that Hume vigorously denied was the claim there are 'pure intellectual ideas.' What I said (about all ideas basically being faint images, whether they are copied from impressions or not) is still a rejection of that rationalist doctrine. In fact, the innate ideas that the rationalists were concerned about (God, substance, mind, etc.) were *all* pure intellectual ideas. So the rationalists wouldn't take the missing shade of blue counterexample as a point in their victory, because that's not the kind of 'innate idea' they were arguing for.

If you think Hume wants to reject the existence of innate ideas in the sense that there are no ideas we are born (or come into existence) with, Hume explicitly says he doesn't care about that:

"If by innate be meant, contemporary to our birth, the dispute seems to be frivolous...what can be meant by asserting, that self-love or resentment of injuries, or the passion between the sexes is not innate?" (E22)

Or rather, if you think he's concerned about the *source* of our ideas, and he wants to prove that all ideas ultimately have their source from things outside our minds, Hume also says he doesn't care about that:

"As to those impressions, which arise from the senses, their ultimate cause is, in my opinion, perfectly inexplicable by human reason, and 'twill always be impossible to decide with certainty, whether they arise immediately from the object, or are produc'd by the creative power of the mind, or are deriv'd from the author of our being. Nor is such a question any way material to our present purpose." (T84)

Hume is rather tricky, because he says that he's settling the old question about whether there are any innate ideas, but he's actually completely changing the nature of the question. I recommend reading Nancy Kendrick's paper on this topic.

In essence, that question is also what my brother is studying. Modeling human vision via computers (and investigating to what extent that is possible) is my brother's main area of research (if I understand correctly what he does).

I remember talking about this in my Modern Philosophy class with Derk Pereboom (one of the best professors I've ever had to be honest). When this example was brought up during the course of the semester, I really never understood what the fuss is about. These colors are really composed of a complex interaction of things (DM has already pointed some out in an earlier post) such as photon frequency and the interactions with different rods and cones in the eyes. I could be off but I'd assume that Massimo is on to something when he mentions its not a serious threat, though I think for reasons other than it being "contrived."

Well, if color ideas are complex rather than simple (which is what I think you're implying) then the situation simply isn't a counterexample to Hume's principle in the first place, so there's no problem at all.

But that's not really the mystery. The mystery is, *given* that Hume seems to think that it is a counterexample to his principle (or, at least, a hypothetical counterexample), why did he think he could just ignore it without a second thought? Using modern science to show that is wasn't actually a counterexample doesn't help answer *that* question, because obviously Hume didn't know any of that stuff.

The mystery is less about nature of the color experiment and more about Hume's methodology for dealing with counterexamples to general principles.

Massimo. Great article. I think the following passage by Bertrand Russel is very relevant here.

"British philosophy is more detailed and piecemeal than that of the Continent; when it allows itself some general principle, it sets to work to prove it inductively by examining its various applications. Thus Hume, after announcing that there is no idea without an antecedent impression, immediately proceeds to consider the following objection: suppose you are seeing two shades of colour which are similar but not identical, and suppose you have never seen a shade of colour intermediate between the two, can you nevertheless imagine such a shade? He does not decide the question, and considers that a decision adverse to his general principle would not be fatal to him, because his principle is not logical but empirical. When--to take a contrast--Leibniz wants to establish his monadology, he argues, roughly, as follows: Whatever is complex must be composed of simple parts; what is simple cannot be extended; therefore everything is composed of parts having no extension. But what is not extended is not matter. Therefore the ultimate constituents of things are not material, and, if not material, then mental. Consequently a table is really a colony of souls.

The difference of method, here, may be characterized as follows: In Locke or Hume, a comparatively modest conclusion is drawn from a broad survey of many facts, whereas in Leibniz a vast edifice of deduction is pyramided upon a pin-point of logical principle. In Leibniz, if the principle is completely true and the deductions are entirely valid, all is well; but the structure is unstable, and the slightest flaw anywhere brings it down in ruins. In Locke or Hume, on the contrary, the base of the pyramid is on the solid ground of observed fact, and the pyramid tapers upward, not downward; "

While I am no Hume scholar, I did have the good fortune of studying Hume under Ted Morris, then an editor of Hume Studies, while I was a grad student in Cincinnati. In his seminar, when confronted with the missing shade of blue, I considered what I take to be a potential reconciliation of the conflict. Given what you pointed out about Hume's recognition of our ability to make complex ideas out of simple impressions, I believe Hume can simply maintain that the missing color is, in fact, just a combination of simpler impressions. In other words, the blue that we recognize as missing, is in fact a combination of two shades of blue we have already experienced.So the blue that I haven't as of yet encountered, is in fact a product of mixing two colors that I have already seen, much like the unicorn that we create out of the various things we have experienced and that provide all of the cognitive content we require.I'm not sure how this fits with Hume's own account of his position, or why he doesn't seem to explicitly state this possibility, but I do believe it can reconcile this inconsistency based on his account of how we create the complex out of the simple.

As a side note, as someone who studied philosophy but doesn't get to do it professionally, you blog and podcasts are something I look forward to always. I admire the relationship you and Julia maintain and the candor that it affords your exchanges, even in the face of disagreement. One of the few things I found uncomfortable about graduate school in philosophy was the counter productive bloodletting that could take place in the seminar room.